1. Field of the invention
The present invention relates to a method of and an apparatus for dyeing relatively small parts molded of synthetic resin, such as slide fastener sliders, snaps, buttons, or the like.
2. Description of the Prior Art
One conventional method of dyeing small parts or objects molded of synthetic resin has been to immerse the parts in a dye liquor. According to such a known dip dyeing process, the dye liquor used is 8 through 20 times, by weight, the objects to be dyed. The objects are accommodated in a perforated casing dipped in the dye liquor, and the cage is rotated or otherwise moved through the dye liquor to dye the objects.
The amount of dye liquor employed in the prior dyeing process is of a bath ratio which is appropriate for the normal dyeing of synthetic fibers which are dyed thoroughly. When the molded parts of synthetic resin are dyed, however, the dyestuff is applied only as thin surface layers to the parts and does not dye the material inside the outer surfaces. The dye solution required is several hundred times, by weight, the dyestuff actually applied to the objects. The degree of exhaustion is therefore quite low, for example 30%. Another problem is that color reproducibility is unstable because of the hydrophilic nature of the dye or the interaction between the synthetic resin objects and the dyeing assistants in the dye liquor. The dyed objects thus tend to differ in color from lot to lot.
The use of the large amount of dye liquor is also disadvantageous in that a cosiderable quantity of dye and dyeing assistants is wasted and an excessive amount of heating steam is consumed.